Generally, cutting insert is fastened to a cutting tool mounted on the machine tool to be used for cutting a workpiece made of iron, non-ferrous metal, non-metal material or the like.
Such cutting insert typically has an upper surface, a lower surface, and a plurality of side surfaces connecting the upper surface and the lower surface. An upper cutting edge is provided between the side surface and the upper surface, and a lower cutting edge is provided between the side surface and the lower surface.
An example of the prior art can be found in Korean Registered Patent No. 10-0949660 which discloses a double-sided cutting insert 10 for use in a milling cutter as shown in FIG. 8, which comprises: two identical opposing end surfaces 12; an outer circumferential surface 14 extending therebetween and comprising two opposing identical major side surfaces 18 and two opposing identical minor side surfaces 16; four spaced major cutting edges 34 each formed at the intersections of the respective end surfaces 12 and respective major side surfaces 18; four spaced minor cutting edges 36 each formed at the intersections of the respective end surfaces 12 and respective minor side surfaces 16; and a major relief surface 50 adjacent the respective major cutting edges 34.
Particularly, the conventional double-sided cutting insert 10 is formed such that, when seen from the end surface 12, as shown in FIG. 10, the major side surface 18 has a generally flat shape, the major cutting edge 34 has a straight line shape and is inclined with respect to the major side surface 18 due to the relief surface 50, and the minor cutting edge 36 has a straight line shape and is perpendicular to the major side surface, according to which the double-sided cutting insert 10 seen from the end surface has a generally rectangular shape. In addition, the conventional double-sided cutting insert 10 is formed such that, when seen from the major side surface 18, as shown in FIG. 11, the major cutting edge 34 has a straight line shape and is inclined with respect to the center line M, according to which the major side surface 18 has a generally parallelogram shape. In addition, when the conventional double-sided cutting insert 10 is seen from the minor side surface 16, as shown in FIG. 9, the minor cutting edge 36 has a straight line shape and is inclined with respect to the center line M. In addition, as shown in FIG. 8, the inner end surface 46 has a shape such that it is closer to a through bore 22 than the major cutting edge 34 and the minor cutting edge 36. That is, the major cutting edge 34 is located higher than the inner end surface 46 serving as a fastening surface.
However, the conventional double-sided cutting insert 10 described above has the problems as described below.
Since the major side surface 18 is generally flat, there is a problem that the cutting load is increased during cutting of the workpiece, which in turn causes a problem that the squareness is reduced.
In addition, when seen from the end surface 12, since the major cutting edge 34 has a straight line shape, there is a limit to increasing the helix angle associated with the cutting performance, which thus causes a structural difficulty in enhancing the cutting performance.
Further, since the double-sided cutting insert 10 seen from the end surface has a generally rectangular shape, there is a problem that the cutting load is increased in the full feeding of workpiece during cutting of the workpiece, which thus causes a problem that the squareness is reduced.
In addition, when seen from the major side surface 18, since the major side surface 18 has a generally parallelogram shape due to the major cutting edge 34 having a straight line shape and being inclined with respect to the center line M, there is a limit to increasing the helix angle associated with the cutting performance, which thus causes a structural difficulty in enhancing the cutting performance.
In addition, when seen from the minor side surface 16, since the minor cutting edge 36 has a straight line shape, there is a structural difficulty in enhancing the surface roughness of the workpiece during cutting process.